Why does my girlfriend always want to be intimate after she watches me play sports?

Essentially, it is her human instincts kickin in. You showed her you were masculine and a virile, capable man on the hockey field. Then in an enclosed space, she could smell your natural body smell (i.e. sweat and hormones -- I know, kinda gross, but very human in an animal sense). For some women, smell does it all. Some women like cologne, other women like the ragged smell of a guy without cologne. So, my suggestion for you is to shower in the morning, don't use cologne, go through the day, and come home at night and see what she does. You could be surprised. Or, when you are in bed, ask her to explain it and ask intriguing questions to her answers. You may get answers and that "dirty" talk may get you both something else. :)